Conventional piston dampers include MR dampers having a tube containing an MR fluid and having an MR piston assembly including a piston which slideably engages the tube and including a rod which has a first end attached to the piston and a second end extending outside the tube. The MR fluid passes through an MR passageway (i.e., a magnetically energizable passageway) of the MR piston. Exposing the MR fluid in the MR passageway to a varying magnetic field, generated by providing a varying electric current to an electric coil of the MR piston, varies the damping effect of the MR fluid in the MR passageway providing variably-controlled damping of relative motion between the MR piston and the tube. The electric current is varied (including turning off the electric current) to accommodate varying operating conditions, as is known to those skilled in the art. The tube and the rod are attached to separate structures to dampen relative motion of the two structures along the direction of piston travel. In one known application, the MR damper is employed as a vehicle suspension damper to control vehicle ride and handling including damping during jounce and rebound.
A known design includes an MR piston having an MR piston core, two MR piston end plates, and an MR piston ring. The two MR piston end plates are attached one each to the two longitudinal ends of the MR piston core. The MR piston ring is attached to the MR piston end plates and is radially-outwardly spaced apart from the MR piston core to define an MR passageway between the MR piston core and the MR piston ring. An MR passageway is a magnetically energizable passageway. An electric coil is located in the MR piston core to magnetically energize MR fluid in the MR passageway. The MR piston core may include an MR bypass passageway (i.e., a magnetically non-energizable passageway) radially inward of the MR passageway and the electric coil. The outer circumference of the metal MR piston ring slidingly engages the inner circumference of the metal tube of the MR damper. Excessive wear on the sliding metal surfaces occurs when high side loads are applied to the MR damper.
What is needed is an improved magnetorheological piston ring and an improved magnetorheological damper having an MR piston ring.